1. Field of the Invention
The present invention is related to a semiconductor integrated circuit and an electric power supply controlling method thereof.
2. Description of the Related Art
As semiconductor manufacturing processes have become handling very fine patterns, leak currents cannot be neglected, while these leak currents flow during waiting statuses where circuits are not operated. The leak currents may constitute one of factors for increasing power consumption of the semiconductor circuits. In order to reduce these leak currents, cutting off power supplies is the most effective method.
A patent publication 1 has described a semiconductor integrated circuit which performs a power supply cutting off operation. The semiconductor integrated circuit described in the patent publication 1 has 2 power supply modes, namely, an operation mode and a standby mode. A power supply domain has been subdivided into a main circuit and a standby circuit. The main circuit contains a CPU to which electric power of the power supply is supplied during only the operation mode. The electric power of the power supply is continuously supplied to the standby circuit. When the standby circuit receives a transfer instruction for transferring the operation mode of the system to the standby mode from the CPU, the standby circuit turns OFF the power supply of the main circuit so as to transfer the system to the standby mode. When an interrupt is issued, the standby circuit holds a factor of the interrupt, and turns ON the power supply of the main circuit. The CPU specifies the interrupt factor held in the standby circuit, and performs a process operation corresponding to this specified interrupt factor.
Also, a semiconductor integrated circuit described in a patent publication 2 contains a power supply domain similar to that of the patent publication 1, and also, does not have such a power supply cutting off circuit, but has a substrate bias control circuit. When the operation mode is transferred to the standby mode, the substrate bias control circuit controls a substrate bias voltage of the main circuit to a high threshold voltage. On the other hand, when the operation mode is recovered from the standby mode, the substrate bias control circuit commences the operation after the high threshold voltage is returned to a zero bias voltage. As previously described, as the method for reducing the leak currents, the substrate bias voltage control operation is carried out, while the power supply cutting off operation is not performed, so that the semiconductor integrated circuit may be recovered to the operation mode in a high speed from the standby mode.    Patent Publication 1: Japanese Patent No. 3724472    Patent Publication 2: JP-A-2004-96073
However, in the above-described electric power supply controlling methods for the semiconductor integrated circuits, when the operation mode is transferred to the standby mode and also the operation mode is recovered from the standby mode, the control operations by the CPU intervene. As a result, the power supply domain containing the CPU must be necessarily required to be brought into the power supply ON status during the operation mode. Although a mode control operation and an interrupt process operation executed between the standby mode and the operation mode do not always require the process operations by the CPU, since the control operations by the CPU intervene, the power supply of the power supply domain (CPU domain) containing the CPU could not be turned OFF during the operation mode. In a system LSI, since such a portion occupied by a CPU domain is large, this occupied area cannot be neglected. As a result, it is very effective to reduce power consumption of the CPU domain.